The present invention generally relates to an intramedullary system for coupling first and second bone portions across a fracture therebetween and, more specifically, to an intramedullary hip pinning system for rigidly interconnecting a femoral head to the remaining portion of the femur and across a fracture in the area of the femoral neck.
The intramedullary nail was introduced in the 1930""s. This device was inserted into the intramedullary canal of the femur resulting in immediate fixation of fractures, early mobilization of the patient, and a lower morbidity and mortality. A number of nails have been introduced for fracture fixation about the femur in proximal end, including the Jewett Nail and Enders Nail.
Intramedullary nails were also inserted down the entire length of the femoral canal to provide a basis for the construct. Threaded wires, standard bone screws or cannulated bone screws were then inserted through or along side the proximal nail and into the femoral head to provide fixation and rotational stability. Compression of the proximal bone fragments against each other was not available and in longer nails the distal tip of the nail tends to rotate out of plane which forces the surgeon to locate the distal screw holes using fluoroscopy by a method commonly known as xe2x80x9cfree-handingxe2x80x9d.
In the 1960s, the compression hip screw was introduced, resulting in improved fixation of the proximal femur. A lag screw assembly was inserted into the femoral head, a plate was attached to the lateral femur, and a compression screw joined the two. These implants provided a more rigid structure for the patient and allowed the surgeon to compress the fractured fragments against each other thereby decreasing the time to mobility. A number of compression hip screws have been introduced for fracture fixation about the proximal femur.
During implantation typical compression hip screws require an incision at least equal to the length of plate being used which extends operative time and blood loss. The side plate also creates a protuberance on the lateral side which provides an annoyance to the patient. Compression hip screw systems also fail to provide adequate compression in oseteogenic patients because the lag screw threads fail to obtain sufficient purchase due to poor bone stock. Poor purchase is known to contribute to nonunion, malunion and the lag screw assembly eroding through the superior bone of the head of the femur in a condition known as xe2x80x9ccut outxe2x80x9d. Additionally, many patients are dissatisfied with the results of compression hip screw surgery because of the excessive sliding to a medial displacement and shortening position which leads to a change in gait.
Newer devices and inventions explored additions to the nail and lag screw assembly to improve the fixation and ease or eliminate the need to locate the distal screw holes. These newer devices are commonly classified as xe2x80x9cexpanding devicesxe2x80x9d and expand in size, after placement, to fill the intramedullary cavity. Freedland, U.S. Pat. Nos. 4,632,101, 4,862,883 and 4,721,103, Chemello, U.S. Pat. No. 6,077,264 and Davis, U.S. Pat. No. 5,057,103 describe a method of fixation which provides points which contact the internal cortical wall. In these patents a mechanism is actuated deploying arms or anchor blades through the cancellous bone to contact the inner cortical wall. These methods are complex, do not deploy through the cortical bone and are difficult to retract should the nail or lag screw assembly require extraction.
Other expanding devices provide surface contact with the internal cortical wall resulting in a wedge effect. Kurth, U.S. Pat. No. 4,590,930, Raftopoulos, U.S. Pat. No. 4,453,539 and Aginski, U.S. Pat. No. 4,236,512 among others have described mechanisms which deploy or expand with a molly bolt concept. These methods are complex and difficult to retract should the nail or lag screw assembly requires extraction and do not deploy through the cortical bone.
Bolesky, U.S. Pat. No. 4,275,717, was the first to discuss engagement within the cortical wall. However, Bolesky""s invention does not address controlled penetration into the wall and required permanent implantation of the actuation rod. In addition, Bolesky does not address the fundamental problem of the actuation rod""s protrusion extramedullarly into the surrounding musculature.
In earlier patents, U.S. Pat. Nos. 5,976,139 and 6,183,474 B1, both incorporated herein by reference, Bramlet describes a surgical anchor which has deployable tangs. These tangs are simple design, internally positioned, yet easily deployed into, and if desired through, the cortical bone providing improved purchase for compression of a fracture; especially in osteogenic bone. These tangs are just as easily retracted should the device require explantation.
In 1988 Lawes, et. al., U.S. Pat. No. 5,176,681, disclosed a method of combining desirable aspects of both intramedullary nails and compression hip screws. Lawes described a method for joining the lag screw and nail to resist loosening or moving of the lag screw during the operation. Approximately 10 years ago Howmedica (Rutherford, N.J., United States) was the first to produce the xe2x80x9cGamma Nailxe2x80x9d, named for its similarity in shape to the Greek letter, as an intramedullary hip compression screw device and other designs soon followed.
In 1990 Durham, et. al., U.S. Pat. No. 5,032,125, disclosed an intramedullary hip compression screw system which incorporated a sleeve for slidably receiving the lag screw. A set screw was then used to engage the sleeve thereby preventing translation and rotation of the sleeve. This device allowed for reduction of the proximal fragment using the same method as conventional hip screw assemblies. Shortly thereafter Smith and Nephew Richards (Memphis, Tenn., United States) produced the xe2x80x9cIntramedullary Hip Compression Screwxe2x80x9d.
These intramedullary hip compression screw systems required a few small incisions, allowed capture of the most proximal fragments of the femur, rigid fixation of the most proximal and distal fragments, and a sliding lag screw assembly which allows reduction of the fragments as the patient ambulates or begins to bear weight on the fractured limb. These nails are typically held in place on the distal end through interference forces with the intramedullary canal and through the use of locking screws.
The typical intramedullary hip compression screw""s shape accommodates the relative shape of the greater trochanter and femoral shaft, neck and head fragments. Therefore, the shape of the hip is preserved. Indications for use of a compression hip screw are expanded because fractures to the subtrochanteric region of the proximal femur, as well as reverse obliquity fractures can be treated more efficiently. Additionally, the bulk of an intramedullary hip screw blocks excessive sliding of the proximal fragment.
Current intramedullary compression hip screw systems continue to suffer from some of the same problems exhibited in those of its predecessors. Osteogenic bone still provides a poor medium for purchase of the lag screw assembly thread inhibiting adequate compression and rotational stability. Longer nails continue to see the distal tip of the nail rotating out of plane forcing the surgeon to locate the distal screw holes by the free-hand method. The free-handing technique leads to an increased surgical time and exposes the surgeon and patient to increased radiation dosages.
Current intramedullary compression hip screw systems also provide new limitations that hamper their effectiveness. One such limitation is evident in both Lawes"" and Durham""s designs. These designs require the use of a set screw to prevent rotation of the lag screw; the set screw in the Lawes patent interacts directly with the lag screw, while Durham""s is indirect with the lag screw. To ensure proper mating takes place the Smith and Nephew Richards"" systems provides a torque wrench, while Howmedica""s system requires tightening of the set screw to full engagement and then backing it off. Over time, loss of calibration of the torque wrench and improper engagement by the surgeon user could lead to an unsatisfactory engagement and decreased usefulness.
Clearly a need exists for a system that is superior to the conventional compression hip screws while minimizing the surgical insult to the human body.
Therefore, it is an object of this invention to teach a simple, effective and controllable fixation device which allows greater purchase of the lag screw assembly within the femoral head resulting in improved compression across the fracture line.
It is another object of this invention to teach a system with rotational stability both in the femoral head and in the femoral shaft, and that offers to minimize, if not eliminate the need for additional distal incisions to locate and place locking screws.
It is yet another objective of this invention to teach an intramedullary hip nail system that provides for a more positive, and more repeatable engagement mechanism for allowing the lag screw to slide during fracture reduction and healing.
It is a further objective of this invention to teach a system designed to allow the surgeon a choice of penetration distance within the femoral head and femoral shaft fixation based upon the injuries presented and the desired level of treatment.
It is a still further objective of this invention to teach a system that allows explantation to occur as easily as implantation.
An intramedullary nail system for coupling first and second bone portions across a fracture therebetween may be provided as a kit of several assembled subassemblies. The subassemblies of the intramedullary nail system according to the invention are combined for installation within the medullary canal of a fractured bone, such as a femur.
In one embodiment of the present invention, the intramedullary nail system includes an intramedullary nail body having an internally threaded trailing end and a leading end with portals which allow passage of cortical screws. The nail body has a transverse bore near the trailing end in communication with the cannulated axial bore for recieving a lag screw assembly. The lag screw assembly has a leading end with an externally threaded portion with portals which allow passage of anchoring tangs and internally deployable and retractable anchoring tangs. The lag screw assembly has internal threads on the trailing end. A slotted sleeve slidably passes through the transverse clearance bore of intramedullary nail and freely telescopes over the lag screw assembly while preventing rotation of lag screw assembly, but allowing axial translation of the lag screw. A compression screw has a shoulder contacting the trailing end of the slotted sleeve and engages the internal threads of the lag screw assembly trailing end providing axial translation of the lag screw assembly within the sleeve. A sleeve lock passes through the axial bore of the intramedullary nail and along the slotted sleeve through its slot(s) thereby preventing rotation and axial translation of the sleeve, but allowing axial translation of the lag screw assembly. An end cap assembly with external threads engages the internal threads of the trailing end of the intramedullary nail.
A preferred embodiment combines the intramedullary nail, the sleeve lock and the end cap assembly into an intramedullary nail assembly. When presented as such, the surgeon or surgical assistant will not have to enjoin these items during the surgical procedure.
The end cap assembly preferably contains a patch of ultra-high molecular weight poly-ethylene (UHMWPE) within the threads. This provides constant positive engagement between the end cap external threads and the intramedullary nail internal threads.
With the intramedullary nail placed into position within the intramedullary canal the lag screw assembly is then placed into position in a manner consistent with common technique. The unique tang assembly is actuated and the tangs are deployed to any desired position thereby achieving the desired level of fixation based upon the quality of the bone.
The lag screw assembly preferably contains a permanently placed anchoring tang assembly stored in a retracted position within the leading end. The tangs are deployed or retracted from the trailing end of the lag screw assembly.
The slotted sleeve is coaxially inserted over the lag screw assembly""s trailing end and through the intramedullary nail. The slotted sleeve is aligned to accept the sleeve lock.
The sleeve lock is actuated via a mechanism in the intramedullary nail insertion instrument. The sleeve lock moves from its primary position to its final position. In its final position the sleeve lock passes through the slotted sleeve slots preventing rotation and axial translation of the slotted sleeve.
The compression screw passes through the sleeve and engages the lag screw assembly. As the compression screw is tightened the lag screw assembly and associated first bone portion are pulled against the intramedullary nail and second bone portion resulting in compressive forces being applied across the fracture.
The compression screw preferably contains a patch of ultra-high molecular weight poly-ethylene (UHMWPE) within the threads. This provides constant positive engagement between the compression screw external threads and the lag screw assembly internal threads.
The cortical screws are then placed into position through the bone and through the intramedullary nail in a manner consistent with common technique.
In another embodiment of the present invention the intramedullary nail system includes a intramedullary nail with portals at the leading end which allow passage of cortical screws and/or anchoring tangs. When the intramedullary nail is placed into position the anchoring tang assembly is actuated to deploy the tangs out from their stowed position into the cortical bone. The tangs are deployed to any desired position thereby achieving a desired fixation and rotation prevention based upon the quality of the bone. Should the system require additional load carrying capability, cortical screws may be placed to enjoin the intramedullary nail with the surrounding cortical bone.
The intramedullary nail of this alternate embodiment is preferably cannulated to allow passage of one or more anchoring tang assemblies. These anchoring tang assemblies are inserted from the trailing end towards the leading end and the tangs deployed by means of an actuator driver. An alternate embodiment of the intramedullary nail has a retracted anchoring tang assembly, which is permanently placed within the leading end of the intramedullary nail and is deployed or retracted by means of an actuator driver from the trailing end of the intramedullary nail.
The anchoring tang assembly contains arcurate shaped tangs that are permanently attached to the assembly""s main body. These tangs are initially formed into a prescribed position for storage. As the assembly is actuated, and the tangs deploy, the tangs are formed into their final shape through interaction with the portal of either the intramedullary nail or the lag screw assembly.
The lag screw assembly preferably contains a permanently placed anchoring tang assembly stored in a retracted position within the leading end. The tangs are deployed or retracted from the trailing end of the lag screw assembly.
The anchoring tang assembly within the lag screw is similar in design to that within the intramedullary nail in that it contains arcurate shaped tangs that are permanently attached to the assembly""s tang body. These tangs are initially formed into a prescribed position for storage. As the assembly is actuated, and the tangs deploy, the tangs are formed into their final shape through interaction with the portal of either the intramedullary nail or the lag screw assembly.
The end cap preferably contains a patch of ultra-high molecular weight poly-ethylene (UHMWPE) within the threads. This provides constant positive engagement between the end cap external threads and the intramedullary nail internal threads. In its final position the end cap locks the sleeve and inhibits the sleeve from sliding or rotating out of a prescribed position.
The intramedullary nail system may be supplied as a kit with subassemblies to be combined into the complete system during the surgical procedure.